Heartworm Disease In Dogs

Heartworm disease is a very serious diagnosis and disease in cats and dogs. Heartworms are parasites (worms) that live in the heart, lungs and blood vessels in dogs and cats.

Heartworms, a year-round concern, are transmitted by mosquitos. A mosquito will bite a dog and take a blood meal. If the dog is infected with heartworms, the mosquito will pick up microfilaria (immature worm). The microfilaria will begin maturation in the mosquito over 10 to 14 days. The mosquito then bites another pet and deposits the mature microfilaria (larvae) into that pet’s bloodstream. The larvae travel through the vessels and into the blood supply to the heart and lungs, complete their maturation and develop into worms. It can take 6 months for the larvae to mature into adult worms. Worms can live for years in the heart.

In the early stages of the disease, dogs may not show any signs of disease. As the worm burden increases, dogs can experience exercise intolerance, decreased appetite, weight loss, coughing, cardiac enlargement, lung disease and blood vessel enlargement. The most severe consequence to heartworms is cardiac failure or blockage in the heart and lungs. Dogs can die from heartworm disease.

Treatment for this disease occurs over months and certain medications need to be administered in the hospital setting. Dogs that are being treated need to be on significant exercise restriction for months because as worms are dying, they can break off and cause small blockages.

Because cats are not the desired host for heartworms, heartworm disease in cats is different. Many times, microfilaria do not mature into adult worms and if they do, the numbers are low. This is not to say that this is not a significant concern in cats. Clinical signs in cats include no signs to coughing, anorexia and weight loss. Microfilaria and worms can cause substantial inflammation in the lung tissue resulting in Heartworm Associated Respiratory Disease (HARD) in cats. There is no treatment for heartworms in cats, so prevention is even more essential.

We perform a heartworm/tick born disease test at your dog’s annual exam. This test evaluates for the presence of adult worms only. Remember, it can take 6 months for microfilaria to mature to an adult worm. This means that a dog can be infected with microfilaria but can be negative on a screening test. If your dog has not been receiving prevention for two months (or more) or if you adopt a dog from an endemic area, we recommend retesting them in 6 months.

Testing cats for heartworm can be a difficult task. They can have respiratory damage and microfilaria but can be negative on a test.

The good news is that this disease is preventable!!!!! It is less expensive and safer to prevent this parasite than to treat it. The doctors at Neffsville Veterinary Clinic recommend year-round prevention for dogs with Sentinel Spectrum, a monthly chew. Not only does Sentinel Spectrum prevent heartworms, it also prevents intestinal parasites (roundworms, whipworms, hookworms, tapeworms) that we can get from our pets and also prevents flea eggs and larvae from hatching out in the environment. We recommend that all cats are given Revolution to prevent heartworms, roundworms, hookworms, fleas, and ear mites.